This invention relates to a semiconductor device having a barrier metal layer for suppressing diffusion of any of the elements constituting the interconnects of the device. It also relates to a method of manufacturing such a device.
Generally, a semiconductor device has a barrier metal layer arranged at the bottom or the side sides of the metal interconnects of the device. Such a barrier metal layer prevents mutual diffusion and reaction of the interconnection metal and the silicon diffusion layer, diffusion of the interconnection metal into the interlayer dielectric film surrounding the interconnection layer and reaction of the metals of the via-plug and the interconnection layer if they are made of different metals.
Barrier metal is required to show a sufficient extent of barrier effect of suppressing diffusion and reaction of the metal of the interconnection layer of semiconductor devices in the process of manufacturing the devices and during the operation of the devices due to the electric field and the high temperature existing in the devices. At the same time, it is required to be very thin in such a manner that it may not raise the effective electric resistance of the interconnects. Then, barrier metal showing a low resistivity and a low electric contact resistance has to be used in order not to raise the electric resistance at the contacts and the via-plug. Additionally, it is required to adhere well to the interlayer dielectric film and the interconnection layer.
Monolayer barrier metal of metal nitride such as TiN or TaN is known to show a satisfactory level of barrier effect in known semiconductor devices and have characteristic properties required thereto. However, with the current trend for a higher degree of integration and the use of miniature elements, a very thin barrier metal layer comes to be used in semiconductor devices at the cost of a satisfactory barrier effect.
Additionally, as copper is used popularly for the interconnection layer of semiconductor devices in recent years in an attempt for realizing high speed operation and high reliability, any known barrier metal can no longer provide a sufficient level of barrier effect of preventing copper from rapidly diffusing into the silicon substrate and the dielectric layer. Still additionally, the resistivity and the electric contact resistance of the barrier metal of a semiconductor device are required to become lower in order to make the device operate at higher speed. In short, known barrier metal can no longer provide a sufficient level of barrier effect and electric characteristics.
The insufficient barrier effect of known barrier metal is particularly remarkable in non-aluminum type metal interconnects. This is because the thin aluminum oxide film covering aluminum interconnects operates effectively as a tight barrier film. Such an aluminum oxide film layer is formed as a native oxide particularly along the interface of a metal other than aluminum and an aluminum alloy and conduction of electricity across the interface can take place in the form of tunnelling current because of the small film thickness. On the other hand, while copper, silver, gold and alloys of any of them can be used for interconnection as they show a resistivity lower than that of aluminum, they cannot be expected to form a good oxide layer as in the case of aluminum. Thus, there is a strong demand for a novel barrier metal film that provides a barrier effect better than ever.